Fuel burning apparatus



Dec. 5, 1967 J. M. RACKLEY ETAL 3,356,122

FUEL BURNING APPARATUS Filed Dec. 5, 1964 I 2 Sheets-Sheet 1 FIG.3

' A I BURNER Q 35 37A /4o 28 [63mm 16A 28A 29 Jphn M. Rackley ATTORNEY 1967 J. M. RACKLEY ETAL 3,356,122

FUEL BURNING APPARATUS Filed Dec. 5, 1964 2 Sheets-$heet 2 S O J LL.

O 0 I l I I Tfi 100 JMMIJJ vo BURNER LOAD I United States Patent f 3,356,122 FUEL BURNING APPARATUS John Martin Rackley, Alliance, and George Mnsat, Canton, Ohio, assignors to The Babcock & Wilcox Company, New York, N.Y., a corporation of New Jersey Filed Dec. 3, 1964, Ser. No. 415,708 5 Claims. (Cl. 1581.5)

This invention relates generally to fuel burning apparatus, and more particularly to an improved burner and control system for burning liquid and/ or gaseous fuel in a furnace combustion chamber.

If the field of steam generators a recent trend has developed toward the total shop fabrication of small to medium sized oil and/or gas fired steam generators for use in schools, hospitals, small factories, etc. In an effort to maximize the steam capacity in these units while staying within the height and width restrictions imposed by transportation facilities, manufacturers have extended the lengths of the shop fabricated steam generators, so that the higher capacity of these units have long and relatively narrow combustion chambers. Typical of this type of unit is a 100,000 pounds of steam per hour generator sold by a leading manufacturer, which unit has a combustion chamber that is approximately six feet wide, ten feet high and 25 feet long.

Steam generators of this capacity are usually equipped with circular fuel burners in which the mixing of fuel and air is primarily accomplished by imparting a large rotational component of movement to the incoming air by means of a register. Burners of this general type are characterized by a short, bushy flame because of the combination of the lateral components of air velocity due to spinning the combustion air and the natural tendency of the flame to expand as combustion proceeds. In a narrow, relatively long, fluid-cooled furnace combustion chamber, the use of such burners may cause severe problems, not only because the short bushy flame produces an uneven heat release pattern Within the furnace, but also because impingement of the flame on the generating tube lining the furnace side walls may cause severe coking or tube burn-out.

Frequently, steam generators of the above-mentioned character are subjected to Widely fluctuating load demands. Furthermore, units of this type are ofttimes equipped with fully automatic control and are expected to operate reliably and safely under these operating conditions without attention for long periods of time. Thus, in adapting a burner for use in conjunction with such a steam generator, it is necessary to provide a totally reliable, preferably simple combustion control system that will safely permit unattended burner operation under the severest of changing' load conditions.

In steam generators of this character, the expense of an air heater is normally not economically justifiable on the basis of efficiency. Thus, the burner is additionally burdened'by the requirement of cold-air burner operation. In the interest of economy, it is also desirable that the burner have a low draft loss so that the cost and power consumption of the combustion air fan may be minimized.

The above noted conditions, considered aggre'gately have continuously thwarted attempts to develop a burner and associated control system optimally suited for use in conjunction with high capacity shop fabricated steam generators. Attempts have been made to use a burner having an axial (as opposed to rotational) air flow pattern to avoid the short bushy flame; however, an axial air flow pattern normally does not provide sufiicient turbulence to effect adequate mixing of fuel and air and the establishment of a stable ignition zone. Moreover, as air velocities are increased to increase turbulence, burner draft loss (and therefore fan size and power consumption) Patented Dec. 5, 1967 increases to an intolerable level. In this regard, it should be noted that burner draft loss theoretically increases as the square of velocity. Thus, if the burner draft loss at an air flow equivalent to /5 of full load air flow is 1 inch w.g., the full load draft loss will theoretically be 25 inches w.g. From these comparison figures, the difficulties in developing an axial flow burner having a reasonable draft loss at full load in addition to a reasonable degree of turbulence to promote mixing effect at reduced loads are readily recognizable.

It is therefore an object of the present invention to provide the fuel burner and associated control apparatus for use in conjunction with a long, relatively narrow combustion chamber of the type normally found in a high capacity shop fabricated steam generator. It is a further object that this burner be of simple, inexpensive construction and capable of burning liquid and/or gaseous fuel over a wide load range, i.e., a load range of 10 to 1, while using ambient temperature air. A still further object of this invention is to provide a simple and reliable control system for this burner so that it will operate over a widely fluctuating load range without attention for extended periods of time.

To attain these objects, according to the present invention there is provided, in combination with a circular port formed in a boundary wall of an elongated furnace, a fuel burning apparatus and associated control system capable of operation over a wide load range and particularly adapted to produce a long, relatively narrow flame to substantially conform to the shape of a furnace chamber. The fuel burning apparatus includes walls forming a windbox outside of the furnace and enclosing the circular port, and a blower for supplying superatmospheric combustion air to the windbox. A partition divides the windbox into a first and second flow chamber. First damper means, associated with the blower, are provided for controlling the total amount of air delivered to the windbox, and second damper means disposed across the flow area of the second chamber are provided for apportioning the flow of air from the blower between the chambers. An open ended substantially cylindrical member, coaxially arranged with respect to the port, has its outer end terminating at the partition, While the other end extends toward the port. A set of substantially radial vanes is disposed in axial alignment with the cylindrical member for imparting a rotational velocity component to the air flowing therethrough from the first chamber through the cylindrical member and thence through the port and into the furnace.

A pair of fixed position spaced frusto-conical members are arranged in concentric parallelism and form therebetween an annular passage coaxially arranged with respect to the port. One end of this passage opens to the second chamber, while its other end opens toward the port so as to direct a non-rotating converging annular stream of air from the second chamber directly to the port and into the furnace. Means are provided for introducing fluid fuel into the port in a pattern symmetrical with respect to the axis of the port and for varying the supply of fuel to the burner in response to the load demands of the furnace. A damper actuating system is also provided for simultaneously adjusting the first and second damper means in response to changes in burner load. Linkages intercom nesting the damper actuating mechanism with the first and second damper means are arranged so that the second damper means attains its fully closed position prior to the first damper means and so that the first damper means opens prior to the second damper means.

The various features which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this Specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there is illustrated and descirbed a preferred embodiment of the invention.

In the drawings:

RIG. 1 is a front view of the integral fan and windbox construction of the fuel burning apparatus of the present invention;

FIG. 2 is a partially sectioned side view of the fan and windbox of FIG. 1;

FIG. 3 is an enlarged sectional side view of the burner which is installed within the windbox of FIGS. 1 and 2 with the burner centerlines designated in FIGS. 2 and 3 being coextensive;

FIG. 4 is a partially diagrammatic view of the control linkage associated with the windbox arrangement of FIGS. 1 and 2;

FIG. 5 is an enlarged end view of the biasing damper shaft shown in FIG. 4;

FIG. 6 is a top view taken along lines 66 of FIG. 5; and

FIG. 7 is a graph showing the proportional distribution of air flow to the windbox chambers over the entire load range.

As shown in FIGS. 1 and 2, the walls forming the windbox 10 enclose the circular opening 11 in the wall plate 12 of the furnace 13. An integral combustion air supply fan or blower 14 is disposed above the windbox 10 and discharges air downwardly thereinto. The windbox 10 is divided into forward and rear chambers A and B respectively by an upright division plate 15 disposed within the windbox 10 parallel to and spaced between the furnace wall plate 12 and the windbox front wall 16. Circular openings 21 and 22, coaxial with the opening 11 in the furnace wall 12 are respectively formed in the division plate 15 and the windbox front wall 16.

The burner assembly of FIG. 3 fits within the windbox 10 as can be readily seen by recognizing that the burner centerlines indicated in FIGS. 2 and 3 are coextensive.

The burner is formed with an outer frusto-conical member 25 connecting at its forward or inner end to a cylindrical collar portion 25A which is suitably attached to the furnace wall at the opening 11 formed in the furnace wall plate 12. An inner frusto-conical member 26 is disposed in concentric parallelism with the outer member 25 to form therebetween an annular space or passage 29 coaxial with the burner centerline and converging toward the furnace 13. The inner end of the inner frustoconical member 26 is connected about its perimeter to a rearwardly extending cylindrical member 27 which is also coaxial with the burner centerline. The outer end of the cylindrical member 27 connects with a spinner vane support frame 28 having a flange portion 28A which is connected to division plate 15 about the periphery of the opening 21. A set of radially disposed spinner vanes 33 are arranged about the burner centerline within the frame 28, and are rotatably connected between the frame 28 and the hub assembly 31. The hub assembly 31 connects to an operating handle 32, disposed outside the windbox 10, and is constructed in a known manner so that movement of the operating handle 32 produces rotation of the vanes 33 to thereby vary the amount of spin imparted to the air flowing from chamber A through cylindrical member 27. The centrally disposed hub assembly 31 is fixed in position by connection to the front cover plate 16A which closes the opening 22 formed in the windbox front wall plate 16. An oil atomizer assembly (or liquid fuel introduction element) 35 of a known type is supported by and extends coaxially into the burner through the hub assembly 31, projecting into and beyond the opening 11 in furnace wall plate 12. Attached to the innermost end of the oil atomizer assembly 35, and spaced downstream from the forward or discharge end of the cylindrical member 27 is an impeller of air deflector 36 of known type. A torous shaped gaseous fuel supply pipe 37 is arranged around the outside of the frame 28 and is fitted with circumferentially spaced generally forwardly projecting spuds 37A suitably formed with openings (not shown) through which gaseous fuel is discharged immediately adjacent the outer boundaries of the impeller 36. An ignitor assembly 38 of known type extends through the front cover plate 16A and the division plate 15 and terminates in the annular space 29.

The furnace front wall 13A, constructed either of refractory material as shown or of fluid-cooled tubes (not shown), is formed with a contoured opening or throat 40. The inlet portion of the throat 40 has a frusto-conical surface 40A converging from the boundaries of the opening 11 toward the furnace 13. The final or discharge portion of the throat 40 is preferably formed with a cylindrical surface 40B, the purpose of which will be described hereinafter.

From the foregoing, it will be noted that two separate flow paths are provided for admitting combustion air from the fan 14 to the burner; viz., the central flow path from chamber A through the cylindrical member 27, and the annular flow path from chamber B through the annular passage 29. This division of air flow between the central and annular flow paths, and the regulation of the proportional amounts of air passing through these flow paths, constitute major features of the present invention. Under actual operation, it has been found that in order to maintain ignition and reasonably stable flame shape control over a wide load range, the quantity of air admitted via the central air flow path must be variably proportioned with respect to the total combustion air supplied by the fan 14 at various loads. Thus at low firing rates, i.e., less than approximately 20% of full load, when air velocities are decreased, a major portion or substantially all of the air must be admitted through the central flow path in order to obtain sufficient mixing action in the immediate vicinity of the fuel discharge from the atomizer 35. Moreover, the spin imparted to the central air flow by the vanes 33 helps to further promote mixing at lower rates. Because of the inherently unstable nature of an unconfined spinning air stream within the furnace, the flow of air through the central portion of the burner must be limited as the total air flow to the burner increases. Thus, if all the combustion air were to be introduced through the center of the burner at full load not only would a ragged unstable flame result, but the draft loss through the burner would be intolerably high due to the aforementioned relation between flow and pressure loss. Accordingly, as the load on the burner is increased, the proportional amount of total combustion air passing through the central air flow path of the burner is decreased, and the air introduced through the annular passage 29 is correspondingly increased. The annular air flow is directed into the flame so that, should its course be unaltered upon leaving the annulus, it would impinge or converge at a point just beyond the exit of the burner throat 40. By thus directing the annular air stream into the flame, more intimate mixing of fuel and air will be obtained. Meanwhile, ignition stability is maintained immediately downstream of the impeller 36 due to the adequate flow of air spinning through the cylindrical member 27. Since the liquid fuel is introduced from the oil atomizer 35 as a diverging conical spray, the converging annular air stream impinges on and penetrates the oil spray droplets at approximately right angles to the spray cone, thereby providing homogeneous mixing of fuel and air to effect complete combustion of the fuel within the furnace 13. It can also be seen that by introducing air through the burner via both the central and annular flow paths, the burner draft loss or pressure drop at full load will be substantially less than if all the combustion air were introduced through the central portion of the burner.

The graph of FIG. 7 indicates a proportioning of air flow that has been found in field tests to be particularly satisfactory in the operation of this burner. According to this operating procedure, at loads below 20% of rated burner load, substantially all of the air is introduced through the center of the burner (chamber A). As the load is increased, the percentage of total air passing through the burner center is decreased, and the remaining percentage, which passes through the annular flow passage (chamber B) is increased, until at full load the higher percentage of the total air is being introduced through the annular passage 29. Operation under these conditions has indicated that the ratio of air flow through the burner center at 20% load and at full load is about 2-to-1, so that ratio of burner draft loss at these two conditions is about 4-to-1. Operating experience has indicated that satisfactory operation is obtained with the vanes 33 set in a single fixed position over the entire load range when firing liquid and/or gaseous fuel. Thus, although the vanes 33 have been described as being rotatable by operation of the handle 32, they actually are preferably mounted in a fixed position, thereby eliminating the vane adjustment feature and consequently reducing the cost of the burner.

The introduction of proportionally increasing percentages of annular air as to burner load increases is important in relation to flame shape control, and is more particularly necessary for producing a long, relatively narrow flame shape required in a similarly shaped combustion chamber to avoid flame impingement on the combustion chamber side walls, After ignition, the flame has a tendency to widen or diffuse because of the centrifugal action of the spinning central air issuing from cylindrical member 27, and because of the natural expansion of the combustion gases as their temperature is sharply increased due to combustion of the fuel. The impinging air introduced through the annular passage 29 counteracts this tendency for expansion and effectively prevents the flame from widening too rapidly. At lower loads, of course, the need for the restraining counteracting effect of the annular air flow is not as great as at high loads. It should be noted that an additional restraint to the rapid widening of the flame is provided by the cylindrical surface 40B at the discharge end of the burner throat 40.

Where, as in the above-described fuel burning apparatus, a centrifugal type fan 14 is integrally connected to the windbox 16, there may result a severeproblem of maldistribution of air flow in the windbox 16 because of the tendency of the air to be concentrated, due to centrifugal force, on the one side (right side of FIG. 1) of the fan discharge. This maldistribution may result in a nonsymmetrical or lopsided flame shape and consequently impingement of the flame on a wall of the furnace 13. The above-described windbox arrangement advantageously tends to rectify this maldistribution problem during operation of the burner in the lower load range. At low firing rates, when the biasing damper 70 is only partially opened, the air from the fan 14 passing into chamber B is deflected by the biasing damper 70 toward either the division plate or the wall plate 12, depending on the direction inrwhich the damper 70 is arranged to open. As a result of the deflections of air between damper 70 and the plate 12 or 15, the air flowing through chamber B is more evenly distributed across the entire width of the windbox 16. At higher loads, as the damper 70 approaches its wide-open position, the deflection of air is less and consequently the dispersing effect of the damper 70 is reduced; however, at these higher loads, the normal burner draft loss is sufliciently high to produce satisfactory air distribution. As to any maldistribution of air to chamber A, the problem is not so severe, since this air is.redistributed by the vanes 33 as it flows into the cylindrical member27. I

Although the fuel burning apparatus has been described herein in terms of the fan 14 being disposed above the burner, it should be recognized that all of the advantages of the split-windbox arrangement could also be realized in installations where the fan is "arranged on either side of or under the burner.

To produce the above described proportioning of air flow between chambers A and B over the burner load range, a simple and reliable control system is integrally incorporated as a part of the fuel burning apparatus. The control system elements are shown generally in FIGS. 1 and 2 to illustrate their preferred placement with respect to the windbox 10 and the fan 14; however, reference should be made to FIGS. 4, 5 and 6 in regard to the following description relating to the operation of the control system, since these latter drawings have been made to show more clearly the relationship of the control system elements. Accordingly, similar parts where shown are labelled with similar reference numbers in FIGS. 1, 2, 4, 5 and 6.

The primary control elements in the air flow control system are the fan inlet damper 41 and the blade-type biasing damper disposed at the top of and arranged to restrict the flow quantity of air to chamber B. It should be noted that chamber A is unobstructed insofar as no adjustable air flow regulating means are provided in the air flow path from the discharge of the fan 14 through chamber A and the cylindrical member 27. As mentioned above, the vanes 33 are preferably fixed in position and are not intended for regulating the flow of air.

The fan inlet damper 41 is of the commercially available radial vane type which is operated from the open to the closed positions by movement of a lever arm 42. By using a fan inlet damper 41, the total air flow through the fan can be varied even though the fan drive motor 14A is of the constant speed type.

The fan inlet damper 41 and the biasing damper 70 may suitably be operated by a transducer control drive mechanism 44 wherein an incoming signal (electric or pneumatic) is converted to mechanical motion. In the drive mechanism 44 shown, the signal imposed on a suitable controller 45 is converted into rotation of the output shaft 44A of the control drive mechanism 44. The controller 45 may suitably reflect a demand for increased heat input to the furnace 13. For example, in a steam generator, a signal representing the demand for increased or decreased steam output would be transmitted from the controller 45 to the drive mechanism 44. The drive mechanism 44 would then convert this signal into a precalibrated amount of rotation of the shaft 44A in the direction corresponding to the motion required to effect the air flow change necessary to increase or decrease the fuel input to the furnace 13. The shaft 44A of the drive mechanism 44 connects to a drive arm 46 which in turn is connected by the linkages 47 and 48 respectively to the lever arm 42 by which the fan inlet damper 41 is operated, and to the biasing damper lever 50 through which the biasing damper 70 is rotated.

From FIG. 4, wherein the fan inlet damper 41 and biasing damper 70 are shown in their closed positions, it can be seen that as the shaft 44A rotates clockwise in response to a signal from controller 45 requiring increased air flow, the drive arm 46 moves downwardly to the position indicated at 46, and the linkages 47 and 48 are moved downwardly due to their connection to the drive arm 46. The downward movement of the linkage 47 causes clockwise rotation of the drive arm 42 to the position indicated at 42', at which position the fan inlet damper 41 opens, thus increasing the total air flow to the windbox 10. Meanwhile, the downward movement of the linkage 48 causes clockwise rotation of the biasing damper lever 50 to the position indicated at 50", thereby opening the biasing damper 7! to admit a greater portion of the air flow from the fan 14 into chamber B.

As already stated, it is desirable that the biasing damper 70 remain closed when the burner is operating at or below 20% of full rating so that substantially all of the air flows through chamber A and the central portion of the burner throughout this portion of the load range.

To accomplish this result, a mechanical lag device is built into the control components by which the biasing damper 70 is rotated. The lag producing elements are shown in FIGS. and 6. The shaft 60 to which the biasing damper 70 is rigidly connected is provided at its one end with a generally circular cam 61 which is also rigidly keyed or otherwise fixed to the shaft 60. An arcuate recess or notch 61A is formed in the cam 61. Spaced adjacent the cam 61 is a circular collar 65 having secured thereto a laterally projecting pin 68 which is in register with the notch 61A. The collar 65 fits loosely on the shaft 60 and is held in place adjacent the cam 61 by a retaining ring 67 that is rigidly keyed to or otherwise fixed to the shaft 60. The biasing damper lever 50 is attached to the outer surface of the collar 65, and a counterweight 62 is similarly attached to and projects substantially radially from the cam 61 in the general direction shown in FIGS. 4 and 5.

'To demonstrate the operation of the lag mechanism, again referring to FIGS. 4 and 5, as the shaft 44A of the drive mechanism 44 rotates clockwise opening the fan inlet damper 41, the biasing damper lever 50' also rotates clockwise as described above. The motion of lever 50 causes the collar 65 to rotate; however, because the pin 63 is at the extreme position in the notch 61A in the cam 61, during the initial rotation of the collar 65, the cam 61 does not rotate. When the collar 65 has rotated to the extent that the pin 63 moved to the position 63 shown in FIG. 5 and engaged the opposite side of the notch 61A, further motion of the collar 65 will cause the biasing damper 70 to open to the position shown at 70'. The counterbalancing weight 62 maintains the damper 70 in its closed position as long as the pin 63 is so positioned in the notch 61A that it will not exert a force at the right hand end of the notch 61A as shown at 63' in FIG. 5.

From the above it can be seen that during the initial opening of the fan inlet damper 41, air is admitted to the windbox however, due to the rotation of the collar 65 relative to the cam 61, the biasing damper 70 remains closed so that substantially all of the air is constrained to flow through chamber A. The biasing damper 70 is purposely constructed so that it does not seal tightly when closed, thereby allowing a nominal amount of air to bypass the damper 70 and flow through chamber B to prevent the back flow of hot combustion gases and/ or unburned fuel through the annular passage 29. As the fan inlet damper 41 is further opened, the biasing damper 70 also opens, thus effecting a change in the apportionment of the total air flow between chambers A and B. Likewise, when the air flow is being decreased, the biasing damper 40 will reach its closed position before the fan inlet damper 41 closes. It should, of course, be recognized that the amount of mechanical lag as well as the relative rates at which the dampers 41 and '70 open may be changed by varying the extent of the notch 61A and by adjusting the lengths of the various drive arms and linkages.

It can be seen that the above described burner and associated control mechanism provide a simple and reliable fuel burning apparatus that is capable of operation and widely varying load conditions without constant attention by operating personnel. Moreover, this burner, operated in the manner described above, provides flame shape control commensurate with the needs of a modern, high capacity, package-type steam generator requiring a long, relatively narrow, stable flame shape.

While in accordance with the provisions of the statutes there is illustrated and described herein a specific embodiment of the invention, those skilled in the art will understand that changes may be made in the form of the invention covered by the claims, and that certain features of the invention may sometimes be used to advantage without a corresponding use of the other features.

What is claimed is:

1. In combination with a boundary wall of a furnace having a circular port formed therein, fuel burning apparatus comprising walls forming a windbox outside of said furnace and enclosing said port, a blower attached with said windbox for supplying superatmospheric combustion air thereto, first damper means associated with said blower for regulating the total quantity of said air, means forming a central flow path of circular cross-section coaxially arranged with and having its discharge end opening to said port, means for imparting a rotational velocity component to the air flowing through said central flow path, means defining an annular symmetrical converging fiow path coaxially arranged with respect to said port for discharging into said port a non-rotating converging stream of air enveloping the air discharged from said central flow path, second damper means disposed within said windbox for apportioning the flow of air from said blower between the central and annular flow paths, means for introducing fluid fuel into said port in a pattern substantially symmetrical with the axis of said port, and control means for positioning said first and second damper means over the load range of the burner, said control means including a controller from which a signal representing load change demands on said furnace is transmitted, damper actuating mechanism connected to said controller and responsive to said signal, linkages connecting said damper actuating mechanism to said first and second damper means, said linkages being arranged for the simultaneous opening and closing of said first and second damper means in response respectively to the load increase demands and load decrease demands, and means for causing said first damper means to open prior to and to close after said second damper means.

2. In combination with a boundary wall of a furnace having a circular port formed therein, fuel burning apparatus comprising walls forming a windbox outside of said furnace and enclosing said port, a blower attached with said windbox for supplying superatmospheric combustion air thereto, first damper means associated with said blower for regulating the total quantity of said air, means forming a central flow path of circular cross-section coaxially arranged with and having its discharge end opening to said port, means for imparting a rotational velocity component to the air flowing through said central flow path, means defining an annular symmetrical converging flow path coaxially arranged with respect to said port for discharging into said port a non-rotating converging stream of air enveloping the air discharged from said central flow path, second damper means disposed within said windbox for apportioning the flow of air from said blower between the central and annular flow paths, means for introducing fluid fuel into said port in a pattern substantially symmetrical with the axis of said port, and control means for positioning said first and second damper means over the load range of the burner, said control means including a controller from which a signal representing load change demands on said furnace is transmitted, damper actuating mechanism connected to said controller and responsive to said signal, linkages connecting said damper actuating mechanism to said first and second damper means, said linkages being arranged for the simultaneous opening and closing of said first and second damper means in response respectively to the load increase demands and load decrease demands, and mechanical lag means for causing said first damper means to open prior to and to close after said second damper means.

3.,In combination with a boundary wall of a furnace having a circular port formed therein, fuel burning ap paratus comprising walls forming a windbox outside of said furnace and enclosing said port, a blower integrally attached to one wall of said windbox for supplying superatmospheric cotnbnstion air thereto, first damper means associated with said blower for regulating the total quantity of said air, a partition substantially parallel with the plane of said boundary wall dividing said wind box into a first chamber and a second chamber immed ately adjacent said boundary wall, said partition extending toward the wall of said windbox adjacent the blower attachment to said one wall, second damper means including a blade damper disposed only within said second chamber remote from said port and adjacent the end of said partition for apportioning the flow of air from saidblower between said first and second chambers, said blade damper being arranged to laterally deflect the air flowing through said second chamber when the fuel burning apparatus is operating at a reduced load condition, an open-ended member of circular cross-section coaxially arranged with respect to said port and having its one end communicating with said first chamber and its other end opening toward said port, means for imparting a rotational velocity component to the air flowing through said member, means defining an open-ended annular symmetrical converging flow path coaxially arranged with respect to said port and having its one end communicating with said second chamber and its other end terminating immediately adjacent said other end of said member and opening toward said port to direct into said port a non-rotating converging stream of air enveloping the air discharged from said member, means for introducing fluid fuel into said port in a pattern substantially symmetrical with respect to the axis of said port, and integrally associated control means connected with said first and second damper means for varying the apportionment of combustion air flow between said first and second chambers over the load range of the burner.

4. In combination with a boundary wall of a furnace having a circular port formed therein, fuel burning apparatus comprising walls forming a windbox outside of said furnace and enclosing said port, a blower integrally attached with said windbox for supplying superatmospheric combustion air thereto, first damper means associated with said blower for regulating the total quantity of said air, a partition dividing said windbox into a first chamber and a second chamber, second damper means dis posed within only one of said chambers for apportioning the flow of air from said blower between said first and second chambers, an open-ended member of circular cross-section coaxially arranged with respect to said port and having its one end communicating with said first chamber and its other end opening toward said port, means for imparting a rotational velocity component to the air flowing through said member, means defining an open-ended annular symmetrical converging flow path coaxially arranged with respect to said port and having its one end communicating with said second chamber and its other end opening toward said port to direct into said port a nonrotating converging stream of air enveloping the air discharged from said member, means for introducing fluid fuel into said port in a pattern substantially sym metrical with respect to the axis of said port, and intcg rally associated control means for varying the apportion ment of combustion air flow between said first and sec ond chambers over the load range of the burner, said con trol means including a controller from which a signal rep resenting load change demands on said furnace is trans mitted, damper actuating mechanism connected to said controller and responsive to said signal, linkages connecting said damper actuating mechanism to said first and second damper means, said linkages being arranged for the simultaneous \opening and closing of said first and second damper means in response respectively to the load increase demands and load decrease demands, and mechanical lag means for causing said first damper means to open prior to and to close after said second damper means.

5. In a circular burner having means forming a central air flow path discharging a rotating stream of air into a circular burner port and means forming an annular air flow path arranged to discharge a non-rotating stream of air into the port enveloping the air discharged from the central air flow path, the method of operation compris ing the steps of increasing the total air flow through the burner in response to load demand increases, and vary ing the apportionment of air flow between the rotating central and non-rotating annular air flow paths over the burner load range so that at low loads substantially all of the combustion air passes through the central air flow path, at some intermediate load the flow of air is evenly divided between the central and annular flow paths, and at full load the greater portion of combustion air is passing through the annular flow path.

References Cited UNITED STATES PATENTS 1,754,433 4/1930 Peabody 158--115 2,818,109 12/1957 Voorheis l58l1 X 3,049,173 8/1962 Costello et al l58-l1 X FREDERICK L. MATTESON, In, Primary Examiner.

JAMES W. WESTHAVER, Examiner.

FAYQRS, Assistant Examiner, 

1. IN COMBINATION WITH A BOUNDARY WALL OF A FURNACE HAVING A CIRCULAR PORT FORMED THEREIN, FUEL BURNING APPARATUS COMPRISING WALLS FORMING A WINDBOX OUTSIDE OF SAID FURNACE AND ENCLOSING SAID PORT, A BLOWER ATTACHED WITH SAID WINDBOX FOR SUPPLYING SUPERATMOSPHERIC COMBUSTION AIR THERETO, FIRST DAMPER MEANS ASSOCIATED WITH SAID BLOWER FOR REGULATING THE TOTAL QUANTITY OF SAID AIR, MEANS FORMING A CENTRAL FLOW PATH OF CIRCULAR CROSS-SECTION COAXIALLY ARRANGED WITH AND HAVING ITS DISCHARGE END OPENING TO SAID PORT, MEANS FOR IMPARTING A ROTATIONAL VELOCITY COMPONENT TO THE AIR FLOWING THROUGH SAID CENTRAL FLOW PATH, MEANS DEFINING AN ANNULAR SYMMETRICAL CONVERGING FLOW PATH COAXIALLY ARRANGED WITH RESPECT TO SAID PORT FOR DISCHARGING INTO SAID PORT A NON-ROTATING CONVERGING STREAM OF AIR ENVELOPING THE AIR DISCHARGED FROM SAID CENTRAL FLOW PATH, SECOND DAMPER MEANS DISPOSED WITHIN SAID WINDBOX FOR APPORTIONING THE FLOW OF AIR FROM SAID BLOWER BETWEEN THE CENTRAL AND ANNULAR 